1. Field of the Invention
The present invention relates to a pilot operated directional control valve in which a pilot pressure acts on a diaphragm to control a fluid connection between valve ports.
2. Description of Related Art
U.S. Pat. No. 4,516,605 discloses a basic construction of a known pilot operated directional control valve which has a diaphragm on which the pilot pressure acts, as shown in FIGS. 9-13.
In FIGS. 9-13, the pilot operated directional control valve has a diaphragm 11 which also serves as a gasket and which is located between a passage block 20 and a control block 10. The passage block 20 has therein a single feeding port 22 which is connected to a pressurized fluid source (pneumatic pump) P, a pair of loading ports 25, and a pair of discharge ports 27.
The feeding port 22 has a pair of branch passages 23 connected thereto and bifurcated therefrom. The branch passages 23 are connected to a pair of annular passages 24. The loading ports 25 open into the annular passages 24 at the center portions thereof, and are connected to annular passages 26. The discharge ports 27 open into the annular passages 26 at the center portions of the latter. The annular passages 24, the loading ports 25, the annular passages 26 and the discharge ports 27 open into the end face of the passage block 20 adjacent to the control block 10 and face the diaphragm 11. The loading ports 25 are connected to an actuator A. The discharge ports 27 open into the atmosphere.
The actuator A shown in FIGS. 9-13 is a pneumatic cylinder device which has cylinder chambers S1 and S2 which are separated from each other by a piston P1 and which are connected to the respective loading ports 25.
The end portions of the wall which defines and surrounds the loading ports 25 and the discharge ports 27 form on the control block side valve seats 25s and 27s on which the diaphragm 11 is selectively seated. The numeral 12 designates grids which prevent the diaphragm 11 from deforming to bend into the loading ports 25 (and the discharge ports 27) due to a pressure difference across the diaphragm 11.
The control block 10 has therein pilot pressure passages 31 and 32 which open into the center portions of the diaphragm cavities corresponding to the loading ports 25 and the discharge ports 27, respectively. The diaphragm 11 deforms so that it is bent toward the passage block 20 when the diaphragm 11 is subject to a predetermined pilot pressure p through the pilot pressure passages 31 and 32 which are connected to a pilot pressure control device 33. Namely, when the pilot pressure p acts in the pilot pressure passages 31, the diaphragm 11 deforms so that the fluid connection between the feeding port 22 and the loading ports 25 is broken and when the pilot pressure p is exerted in the pilot pressure passages 32, the diaphragm 11 deforms so that the fluid connection between the loading port 25 and the discharge ports 27 is broken. Thus, the fluid connection between the ports can be switched by controlling the feed of pilot pressure into the pilot pressure passages 31 and 32, so that the feed of the working fluid to the actuator A can be controlled, as shown in FIGS. 9-12.
The passages and the ports, shown with the references p are under the pilot pressure p, and the ports and the passages without the reference p open in the atmosphere. In FIG. 9, the piston P1 moves in the right hand direction, since the working fluid (air) is fed from the pneumatic pump P into the cylinder chamber S1 through the feeding port 22, the left branch passage 23 and the loading port 25 on the left side. On the other hand, in FIG. 10, the piston P1 moves in the left direction, since the fluid connection is established between the right loading port 25 and the pneumatic pump P. In FIGS. 11 and 12, the piston P1 does not move in either direction.
According to the pilot operated directional control valve as mentioned above and shown in FIGS. 9-12, thanks to the absence of a sliding part, there are many advantages that no lublication is necessary, a large flow of working fluid (air) can be used, and no precise machining needs, etc.
On the contrary, in the pilot operated directional control valve mentioned above, it is necessary to move the diaphragm 11 at two portions thereof located at the center portions of the loading ports 25, and at the discharge ports 27 for each of two pairs of passages consisting of the feeding port 22 (which is common to the two pairs), the loading ports 25, and the discharge ports 27, and accordingly the directional control valve becomes large and complex.
In addition to the foregoing, it has been experimentally found by endurance tests of the directional control valve of the prior art mentioned above that the endurance (or seal effect) of the diaphragm was insufficient.
The inventors analyze the cause of such an insufficient endurance of the diaphragm as follows.
Namely, the diaphragm 11 comes into contact with and separates from the annular valve seats 25s and 27s and the grids 12 located in the annular valve seats, in accordance with the control of the pilot pressure, as mentioned above. The contact between the diaphragm 11 and the grids 12 occur substantially always at the same contact portions of the diaphragm. This restricted contacts cause marks of grids 12 to be made on the diaphragm 11, resulting in a decrease of endurance and elasticity of the diaphragm 11. Furthermore, since the annular seats 25s and 27s are substantially; flush with the grids 12, the grids 12 restricts the smooth and elastic deformation of the diaphragm 11, resulting in an insufficient sealing effect and endurance.
The primary object of the present invention is, therefore, to provide a compact and simple pilot operated directional control valve which can eliminate the drawbacks mentioned above.
Another object of the present invention is to provide a pilot operated directional control valve which has increased endurance and sealing effect.
Still another object of the present invention is to provide a directional control valve which can be selectively used as a three-way valve or a two-way valve by replacing an element of the valve.
In order to achieve the objects mentioned above, according to the present invention, the improvement is focused on the arrangement of the valve ports and the passages (feeding port, loading ports, and discharge ports, etc.) provided in the passage block. Namely, in the present invention, the valve features the ports connecting passages which open into the diaphragm mating end face of the passage block in a concentric arrangement and also the diaphragm that opens and closes said concentric passages at the center portion and at the concentric annular portion respectively.
The diaphragm has a center valve portion and a concentric annular valve portion surrounding the center valve portion, so that the fluid connection between the two adjacent passages can be independently controlled by the center valve portion and the circumferential annular valve portion.
With this arrangement, the directional control valve can be made small and compact. Namely, it is possible to realize small and simple passage block and control block and a simple and small diaphragm, resulting in an easy assembly of a directional control valve. Furthermore, with the arrangement of the present invention mentioned above, since the diameter of the outer fluid passage in cross section can be increased, the slight displacement of the diaphragm causes a large sectional area of the fluid passage, thus resulting in a large flow of the working fluid.
In addition to the foregoing, to increase the endurance of the diaphragm, according to one aspect of the present invention, the diaphragm is provided with an annular bead which is opposed to an annular valve seat provided on the end face of the passage block that is located adjacent to the control block and which comes into contact with and separates from the valve seat due to the pilot pressure acting on the diaphragm. The annular bead of the diaphragm can be pressed against the valve seat with a high contact pressure, so that a high seal effect can be ensured.
Also, according to another aspect of the present invention, means for preventing an excess deformation of the diaphragm is provided. The preventing means can be embodied by a column which is provided in the passage block and which has an end face slightly recessed from the end face of the passage block adjacent to the control block, so that the deformation of the diaphragm is restricted when the diaphragm comes into abutment with the end face of the column.
According to still another aspect of the present invention, the passage block is composed of a main block and another block element which is integrally connected to the main block. Another block element can be used as a discharge block which has a discharge port or an end plate.
By the selective use of the discharge block or the end plate, the directional control valve of the present invention can be selectively used as a threeway directional control valve or a two-way directional control valve. Namely, according to a different aspect of the present invention, there is provided a diaphragm type of pilot operated directional control valve, comprising a pair of opposed passage block and control block, and a diaphragm which is held between the passage and control blocks, said passage block being provided with ports which are connected to respective fluid passages which open into the end face of the passage block adjacent to the control block, said control block being provided with pilot pressure passages which are connected to a pilot pressure control device to exert the pilot pressure on the diaphragm, the fluid connection between the ports can be controlled by the control of the pilot pressure exerted on the diaphragm, wherein the passage block is composed of a main block and a discharge block with a discharge port or an end plate, said main block being provided with a feeding port and a loading port which open into the end face of the passage block adjacent to the control block through two concentric fluid passages, said passage block being provided with a third fluid passage which open into the end face of the passage block adjacent to the control block and which is concentric to the two fluid passages, said diaphragm having a center valve portion and an annular valve portion therearound, so that when the discharge block is connected to the main block, the discharge port of the discharge block can be connected to the third port of the passage block, and when the end plate is connected to the main block, the third port of the passage block can be closed by the end plate.